URL Validate

/*
function check_it() {
var theurl=document.myForm.t1.value;
var tomatch= /http:\/\/[A-Za-z0-9\.-]{3,}\.[A-Za-z]{3}/
if (tomatch.test(theurl))
{
window.alert("URL OK.");
return true;
}
else
{
window.alert("URL invalid. Try again.");
return false;
}
}
*/